DENSO Green Ways: Philosophy and Products

11 January 2006

Matt Matsushita, President and CEO of Japanese auto supplier DENSO, took the opportunity of the Detroit show to explain DENSO’s Green Ways philosophy and some of its products, such as a CO2 air conditioning system and fuel-efficient compressors for hybrids.

In contrast to most of the presentations at the show (the CEO actually took questions from the assembled reporters), Matsushita took pains, in a speech laced with references to zen and Buddhist philosophy, to outline the cultural background behind the company’s approach.

You can understand our environmental philosophy best by knowing the principle of “consideration” in oriental culture. In the western culture, people value individualism as an esteemed trait. In contrast, oriental society places, instead, the utmost priority on “consideration” for the whole world, including nature as well as mankind. Every creature on Earth has it own meaning of existence.

This philosophy leads us to care for our community, our company employees, our society and our environment. In oriental culture, you simply cannot exist as a human without “consideration.”

DENSO (which produced an electric car prototype in 1950), has recently set in place in most recent strategy vision (DENSO EcoVision 2015), the goals of which are:

Expansion of environmental management into group companies;

Product development and design and takes into consideration performance improvement as well as the environment;

As an example, all DENSO manufacturing facilities worldwide, except for new start-ups in their initial phases, are ISO-14001-certified, a voluntary standard for environmental management. (Including, Matsushita said in response to a reporter’s question, DENSO’s facilities in China.)

One of the products to which he pointed as an example was a CO2 car air-conditioning system—the first to use CO2 as a refrigerant.

Air-conditioning systems generally switched refrigerants from chlorofluorocarbon 12 (CFC-12) to hydrofluorocarbon 134a (HFC-134a) when the damage that CFCs were doing to the ozone layer became apparent. HFC-134a is a potent greenhouse gas, however, and governments and auto suppliers are looking for more benign alternatives.

Compared to HFC-134a, the global warming potential of CO2 is much less; a leak from a CO2-based A/C system would be less damaging.

CO2 has excellent cooling and heating capacities, although because of its lower critical temperature—the temperature above which it cannot exist in a liquid state regardless of the pressure—compared to HFC-134a, CO2 A/C systems need to operate at a pressure seven to ten times higher.

DENSO’s CO2 Air Conditioning System. In DENSO’s system, a gas cooler, corresponding to a conventional condenser, cools CO2 refrigerant discharged from the compressor. The CO2 refrigerant is not condensed by the gas cooler; rather it is partially condensed as a result of adiabatic expansion through an expansion valve.

CO2 Air Conditioning System. Click to enlarge.

An internal heat exchanger is provided between the gas cooler outlet and the evaporator to further cool the CO2 refrigerant, discharged from the gas cooler, by exchanging heat with refrigerant flowing at the low-pressure side of the system. The internal heat exchanger increases the amount of liquid refrigerant at the inlet of the evaporator to increase the cooling performance, resulting in increased coefficient of performance of the system.

In an HFC-134a refrigerant cycle, the accumulator (receiver) is at the high-pressure side. However, in the CO2 refrigerant cycle, the accumulator is disposed at the low-pressure side, since the CO2 refrigerant cannot exist in the liquid phase at the high-pressure side. Because the accumulator is integrated with the internal heat exchanger and the expansion valve, the structure of the CO2 air conditioning system is more simple and easy to install in a vehicle.

In 2002, DENSO developed a CO2 air conditioning system with a heat pump function for Toyota’s FCHV-4 fuel cell vehicle.

This system can be switched between the heating mode and the cooling mode by opening and closing by-pass valves.

In cooling mode, by-pass valve #1 is opened and by-pass valve #2 is closed. Further, air mix dampers of the interior gas cooler are fully closed. As a result, CO2 refrigerant circulates in the system substantially in the same way as the basic CO2 air conditioning system.

In heating mode, by-pass valve #1 closes, by-pass valve #2 opens, and the air mix door of the interior gas cooler opens. High-pressure and high-temperature CO2 refrigerant discharged from the compressor exchanges heat with air to heat the air while flowing into the interior gas cooler. As needed, the system can dehumidify by closing by-pass valve #2 and controlling the opening degree of expansion valve #2.

The compressor for this system is driven by an electric motor, and the compressor and the motor are hermetically integrated together.

Before DENSO can commercialize the CO2 air conditioning system, cost and weight must be further reduced, and reliability further tested. Furthermore, there are support issues involved, including providing service and maintenance equipment.

On another front, DENSO recently began producing the world’s first 1,800-bar diesel common rail system with piezo injectors, which it jointly developed with Toyota Motor Corporation. The new system uses the highly responsive piezo injectors to attain a shorter injection duration and to atomize more finely the fuel spray, resulting in improved performance.